This application is a national stage application under 35 U.S.C. 371 of International Application (PCT) No. PCT/EP99/00336, filed on Jan. 19, 1999.
1. Field of the Invention
The present invention relates to a process for selective hydrogenation of maleic anhydride (MA) or succinic anhydride (SA) to gamma-butyrolactone (GBL) in the vapor phase using a catalyst comprising a mixed oxide of copper and chromium.
2. Background Art
GBL represents an example of small volume commodity of great industrial interest, because of its increasing demand. The main use of GBL is as intermediate for the synthesis of solvents with lower environmental impact than chlorinated ones, like pyrrolidone and N-methylpyrrolidone. It is also the raw material for the production of N-vinilpyrrolidone and of herbicides, pharmaceuticals and rubber additives. The first works on GBL synthesis appeared since 1940""s, due to the start up of the Reppe process form acetylene and formaldehyde to give 1,4-butanediol (BDO) and then GBL by dehydrogenation. The draw-backs of this process are connected with the fluctuating prices of the raw materials and, mainly, with the hazard and the environmental impact of the use of both acetylene and formaldehyde.
During the second half of this century, other technologies have been studied and the number of patents about GBL production processes alternative to the Reppe process constantly increased.
The availability of maleic anhydride on industrial scale led to the development of new technologies for producing GBL, tetrahydrofurane (THF) or BDO by hydrogenation of maleic anhydride or of maleic anhydride derivatives like maleic acid diesters or succinic anhydride.
The liquid phase hydrogenation of MA to GBL has been employed in commercial production, but never reached great industrial importance.
Many patents describe the vapor phase hydrogenation of maleic anhydride or its esters, but mainly for the production of 1,4-butanediol; for instance WO 86/03189 describe the vapor phase hydrogenation of diethyl maleate to BDO.
WO 86/07358 describes a similar process for GBL production.
From a technological and economical point of view the esters of maleic acid or other maleic acid and/or succinic acid derivatives are less desirable raw materials compared with maleic anhydride.
Many patents describe the direct vapor phase hydrogenation of maleic anhydride to GBL, but none of them is completely satisfactory. Some of these patents claim the use of copper chromites as catalysts (e.g., U.S. Pat. No. 3,065,243) but with unsatisfactory conversion and selectivity. Similar systems were claimed in U.S. Pat. No. 3,580.930 or in EP 332 140 (Cu/Zn/Cr/Al), but none of them is completely satisfactory in terms of GBL yield, productivity, by-products formation and catalyst durability.
The present invention provides a process for the vapor phase hydrogenation of maleic anhydride and/or succinic anhydride to GBL over a catalyst comprising a mixed oxide of copper and chromium.
The catalyst contains 30-80 wt % copper and 20-70 wt % chromium. Preferably the mixed oxide catalyst contains 35-55 wt % copper and 25-45 wt % Chromium. The catalyst may further contain the oxides of Barium and/or Manganese, the Barium or Manganese content thereby being less than 1 wt % chromium. The catalyst may further contain the oxides of barium and/or manganese, the barium or manganese content thereby being less than 1 wt %.
The catalyst composition may further contain inert components, such as, tabletting aids or inert fillers.
Preferred catalysts are commercially available, e.g., from Sxc3xcd Chemie, Germany.
In the active state, the catalytically active oxide material may include some metallic components (e.g., metallic copper) formed in the activation step or during the hydrogenation.
The mixed oxide catalyst is subjected to an activation treatment comprising gradually increasing its temperature from room temperature to 200-380xc2x0 C., preferably from 250-300xc2x0 C., in the presence of a hydrogen-containing gas.
The hydrogen-containing gas in the activation treatment may be a mixture of hydrogen and nitrogen. After the activation treatment the catalyst is ready for use. Activation requires a time varying from 8-48 h, depending on reactor size and design.
The activation of the catalyst is exothermic. In case the reactor does not provide an efficient heat removal the hydrogen-containing gas must be suitably diluted or the space velocity must be increased to control exothermic peaks.
Hydrogen dilution results in longer time for the exothermic phase of activation. Large adiabatic reactors usually require the longest activation times. During operation molten maleic anhydride or succinic anhydride or a mixture thereof is expediently vaporized in a hot hydrogen stream in a mixing section in a mixing section; the mixture is then fed into the reactor packed with the above-described activated catalyst. Optionally the catalyst can be packed between two layers of an essentially inert support material, possibly with the same size and shape of the catalyst. Suitable examples of essentially inert support materials include silica, alumina, silica-alumina compound (e.g. mullite), silicon carbide, steatite and titania.
The reaction pressure is preferably between 1 and 100 bar, more preferably between 1 and 30 bar.
The molar ratio of hydrogen to anhydride in the feed is between 10:1 and 300:1 and more preferably between 40:1 and 230:1. Lower hydrogen to anhydride ratios result in tar formation and short catalyst life, higher ratios penalize the productivity of the catalyst.
The reaction temperature is preferably between about 150 and 350xc2x0 C., and more preferably between 200 and 300xc2x0 C.
As it is well known by those skilled in the art, temperature and pressure range in the hydrogenation reaction depend on the desired product mixture. Increasing temperature will result in the mix containing more THF, while increasing pressure will yield substantial amounts of BDO.